1. Field
The disclosure relates to radial or cross-ply tires.
2. Description of Related Art
Radial tires have gradually found their way into various markets, notably the passenger car tire market. This success is due in particular to the qualities that radial tire technology displays in terms of endurance, comfort and low rolling resistance.
The main parts of a tire are the tread, the sidewalls and the beads. The beads are intended to come into contact with the rim. In a radial tire, each of the main parts that make up the tire, namely the tread, the sidewalls and the beads, has functions clearly separated from one another and therefore has a well known specific makeup.
A radial tire is essentially reinforced by a carcass reinforcement comprising at least one carcass ply making, under the tread, an angle substantially equal to 90° with respect to the circumferential direction of the tire. This carcass reinforcement is surmounted radially on the outside, and under the tread, by reinforcing plies that form a belt.
A cross-ply tire differs from a radial tire through the presence of at least two crossed carcass plies making angles other than 90° with respect to the circumferential direction of the tire. The plies are said to be “crossed” because the angles are of opposite signs from one ply to the other.
It will be recalled that the circumferential direction of the tire is the direction comprised in a plane perpendicular to the axis of rotation of the tire and tangential to the belt reinforcer of the tire.
Following the appearance of radial tires, certain cross-ply tires have also been provided with a belt reinforcer under the tread.
In both these types of tire, the tread, which is in direct contact with the ground, has the notable function of providing contact with the roadway and has to adapt to suit the shape of the ground. The sidewalls, for their part, absorb unevenesses of the ground while transmitting the mechanical forces needed for bearing the load of the vehicle and allowing it to move along.
The belt reinforcer is a reinforcement which needs, on the one hand, to be sufficiently rigid with respect to deformations on the edge so that the tire can develop the cornering forces necessary for steering it, and transmit the driving or braking torque and, on the other hand, to be very flexible in bending, i.e. allow variations of curvature of its plane in order to ensure a sufficient surface area for contact between the tire and the ground.
As a result, the belt reinforcer generally has a composite structure allowing it to offer the required stiffness for a relatively low weight. The belt reinforcer is generally made up of at least two plies at different angles, containing reinforcers, in the form of cables, coated in rubber. The reinforcing elements are crossed from one ply to the other with respect to the circumferential direction and may or may not be symmetric about this direction.
Definition of terms hereinafter:                “longitudinal direction”: direction of running of the tire,        “radially on the inside of”: means on a straight line perpendicular to the axis of rotation of the tire, closer to the axis of rotation,        “radially on the outside of”: means on a straight line perpendicular to the axis of rotation of the tire, further from the axis of rotation,        “equatorial plane or median plane”: plane perpendicular to the axis of rotation of the tire and which divides the tire into two substantially equal halves,        “transverse direction of the tire”: direction parallel to the axis of rotation,        “radial plane”: a plane which contains the axis of rotation of the tire,        “meridian section”: cross section containing the axis of rotation.        
Application WO 2010/115860 A1 already discloses a tire for a passenger car, comprising the following three distinct elements:                a radial carcass reinforcement formed of reinforcers extending from one bead of the tire to the other,        a crown belt which essentially consists of:                    reinforcers parallel to the circumferential direction of the tire intended to provide hooping, and            a stiffening layer which essentially consists of reinforcers of the thermoplastic polymer type, in the form of strips coated with rubber, the strips forming an angle comprised between 10° and 80° with the circumferential direction of the tire.The strips are defined as having, when viewed in cross section, a width at least equal to five times their maximum thickness.                        
This tire has the notable benefit of being more lightweight than the tires of the prior art, while at the same time maintaining very good cornering stiffness.
It will be recalled that the cornering stiffness of a tire has a decisive influence over the transverse stability of the vehicle. The higher the cornering stiffness, the greater the cornering force at a given cornering angle. Remember that the cornering angle is defined as the angle of the plane of the wheel with respect to the path followed by the tire.
Thus, the nature and location of the belt reinforcing components are decisive parameters in the cornering stiffness and therefore have a decisive influence over the cornering force of the tire. Now, that earlier patent application WO 2010/115860 A1 proposes a novel design regarding the nature and layout of the belt reinforcing components, that allows the tire to be lightened while at the same time maintaining good cornering force results.